The invention relates to an ice-breaking ship, and more particularly, to the form of the bow portion of the ship.
The bow portion of a ship is usually rather sharp, and up to now also the bow of ice-breakers and corresponding ships has been made sharp. The object of making the bow sharp has been to keep the resistance of movement in water at a low level, and to improve the ice breaking properties of the ship, since the general opinion has been that a sharp bow breaks the ice better in front of the ship.
However, this assumption is not quite correct. It is certainly true that a sharp bow crushes the ice well, but on the other hand, the breaking of the ice by means of bending the ice downwards requires less power than the crushing of the ice to small pieces. In an ordinary ice-breaker the side portions of the bow break the ice by bending it downwards, but exactly at the stem a zone is formed where the ice does not break due to bending, but is crushed and sheared into pieces, due to the advancement of the sharp bow.
It has been shown that a ship accoding to the invention uses in average considerably less energy to break the ice than a ship provided with a traditional ice-breaking bow. In this connection it should be noted that in Finnish patent specification No. 50400, a round bow form has been suggested for an ice-breaking ship, but this kind of round bow differs considerably from the invention, because a bow according to the invention has considerably better ice-breaking properties than a traditional bow, but the earlier suggested round bow does not have better ice-breaking properties than a traditional bow. The advantages of the round bow are based on the fact that the displacement increases while the outer dimensions and the ice-breaking properties remain unchanged.